Ballistic separators are used to separate materials based on mechanical properties. A paddle is typically attached to two synchronized crankshafts such that the paddle moves in a circular or elliptical motion. The paddles form a bed that is typically angled upward, and angled cleats are added to the surface. Each adjacent paddle is typically rotationally offset so that the paddles move into the forward phase in series instead of moving together. The forward toss of the ballistic separator will move a fraction of the material—flat and flexible materials—up the paddle once per revolution, moving from cleat to cleat, while round, heavy or voluminous materials (a second fraction) will bounce off the paddles and not engage the cleats. This “rolling” fraction then bounces off the back lower edge of the inclined bed, separating the flat and rolling fractions. Typically, the paddles will also have sizing grates built in, such that materials smaller than the grate size will pass through the paddle rather than moving up or down.
Due to the need to engage the flat and flexible materials with the cleats and paddles, there is an upper limit to how quickly the paddles can rotate before the material disengages and no longer climbs the paddles. This limits the rotational speed of the paddles, which in turn limits the surface velocity of the flat fraction as it climbs the machine and moves forward once per revolution, putting an upper limit on the capacity of the machine to process flat material. In addition, the higher the bed is angled, the better it is at bouncing the rolling fraction backward, increasing separation efficiency. However, the higher the angle of inclination, the more difficult it is for flat material to climb, as it reduces the throw distance, and there is a chance that material will not climb to the next cleat with every rotation, further decreasing throughput. At some angle of inclination, flat material will no longer climb the bed, and all material will fall off the back.
Ballistic Separators are known to be of low cost to operate per hour in comparison to machines of similar function, such as disc screens. However, their limitations in throughput and efficiency limit their utility and increase their operational cost per volume processed rather than per hour operated. An invention to increase the throughput of the machine would allow for a combination of low operating cost, high throughput, and high separation efficiency.
For example, when processing recyclable packaging material consisting of a mixture of paper, corrugated containers, plastic bottles, and metal cans, glass and finds, and other residual items such as film plastics, a typical ballistic separator will have an input capacity of around 7 tons per hour, of which approximately 4 tons per hour is flat material such as paper and film plastic. Such a machine will typically have eight paddles, each of which is about a foot and a half or half a meter wide, for an overall width of around 12 feet or four meters. An equivalently sized disc screen, processing the same material, will have an input capacity of around 16 tons per hour.
Different paddles and cleat configurations can be used to attempt to increase either throughput or angle of inclination. For example, longer cleat spacing will allow material to move further up the paddle with each rotation, increasing throughput, but will also limit the angle of inclination of the paddles, decreasing separation efficiency. Taller cleats can be used to increase the angle of inclination of the paddles, but flat material will struggle to climb over the cleats, decreasing throughput.
There have been attempts to increase the travel speed of flat materials beyond what is generated by the rotation of the paddles. Most notably, fans are added to the back of the paddles in an attempt to blow flat materials forward, increasing throughput or angle of inclination, as the flat material moves further forward with each rotation. However, this has met with limited success, as paddles are typically around 20 feet or 6 meters long, and air pushed by a fan will disperse before reaching the upper end of the paddle, so that the throughput and separation efficiency of the machine is greater toward the back than toward the front, and material will tend to accumulate as it slows down, therefore limiting the machine to the mechanical properties of the unassisted region.
Other attempts have focused on making the machine wider. For example, there was a 10 meter wide machine produced. However, the amount of torque required from the output gearbox grows linearly with the number of paddles, while the diameter of the crankshaft is still limited to what will fit below the paddles. More room can be created by increasing the displacement radius of the crankshaft; however, this will increase radial forces and momentum on the mechanical components of the shaft. The above machine quickly destroyed itself due to the forces of the machine. Currently, the widest commercially available machine is about eight meters wide. Making a machine that wide creates further problems, as material must be fed to and gathered from the machine from multiple points, creating issues with integrating the machine and driving up the expense of installing the machine. Moreover, the crankshafts get much more expensive as they grow in diameter, creating further expense issues. The above eight-meter wide machine still has less throughput than a typical disc screen.
What is therefore needed is a novel ballistic separator that overcomes these deficiencies.